A cathode-ray tube is evacuated to a very low internal pressure and, accordingly, is subject to the possibility of implosion due to the stresses produced by atmospheric pressure acting on all surfaces of the tube. This problem has been addressed in the art by providing the CRT with an implosion protection band. Such a band is used to apply a compressive force to the sidewall of a faceplate panel of the CRT to redistribute some of the forces. The redistribution of the forces decreases the probability of an implosion of the tube by minimizing tension in the corners of the panel. An implosion protection band is also beneficial because it improves the impact resistance of the tube. Glass in compression is stronger than glass which is in tension, and the band causes compression in panel areas which otherwise would be in tension. Additionally, in the event of an implosion, the redistributed stresses cause the imploding glass to be directed toward the back of the cabinet in which the tube is mounted, thereby substantially reducing the probability of someone in the vicinity of the imploding tube being injured.
The implosion protection band may be a so-called shrinkfit band, or a tension band which is applied either directly to the tube or to a pair of substantially U-shaped rimbands that overlie the sidewall of the faceplate panel.
As the size of color television tubes increase, the stress produced by atmospheric pressure acting on the larger tubes also increases, resulting in the need for implosion protection bands that can apply a greater compressive force to the sidewall of the panel. One method of increasing the compressive force is to increase the cross-sectional area of the implosion protection band. However, this adds additional cost to the tube. A cost efficient way to increase the effective cross-sectional area of the band is to fold over at least a portion of the metal strip used to make the band, to provide a double thickness of band material.
A disadvantage of forming a double thickness band in this manner is that in some tube configurations it is necessary to attach the mounting lugs, which are used to mount the tube within the television receiver, to the double thickness portion of the band. Welding is the preferred method of attaching the mounting lugs to the band; however, the double thickness of material may shunt a portion of the welding current, resulting in higher energy welding requirements and splattering of a rust-inhibiting layer provided on the band. Consequentially, a reduction in the reliability of the weld occurs.